1. Field of the Invention
The present invention relates to a switching device and, more particularly, to a switching device such as an electromagnetic relay, a switch or a timer for switching an electric current in a closed space.
2. Description of the Related Art
As the switching device for closing the electric current in the closed space, there is a closed type relay device (as referred to Patent Publication 1, for example) in the prior art.
[Patent Publication 1]
JP-T-9-510040 (on pages 13 to 17 and in FIG. 1)
As a coil portion 40 is magnetized and demagnetized, more specifically, a plunger 9 is brought into and out of contact with a core center 4 so that an armature assembly 8, as integrated with the plunger 9, and an armature shaft 10 are slit in the axial direction to bring a moving contact disc 21 into and out of contact with stationary contacts 22 and 22.
In the closed type relay device, a core assembly 2 constructing a magnetic circuit includes the core center 4, a core base upper portion 5, a core outer wall 6 and a core base portion 7, all of which are made of a ferromagnetic substance.
However, the core center 4 contacts with the core base portion 7 only through a thin bottomed cylindrical member (although not designated by numeral) but not directly. This bottomed cylindrical member is thought from the viewpoint of magnetic efficiency to be made of a nonmagnetic material. Therefore, the core assembly 2 has a high magnetic resistance so that it requires a high current for achieving a desired driving force. This raises a problem that the power consumption is high.
In view of this problem, the invention has an object to provide a switching device of a low power consumption type.
In order to achieve this invention, according to the invention, there is provided a switching device comprising: a contact mechanism block housed in a closed sealing case; and an electromagnet block arranged outside of the sealing case for driving the contact mechanism block, wherein a pair of iron cores constructing the magnetic block have their one-end magnetic pole portions individually arranged on the bottom face of the sealing case and their other end portions connected to each other by a yoke, so that the two end portions of moving iron member of the contact mechanism block are attracted by and leave the magnetic pole portions of the iron cores as the electromagnet block is magnetized and demagnetized.
According to the invention, the moving iron member of the contact mechanism block contacts with the magnetic pole portions or the one-end portions of the paired iron cores constructing the electromagnet block, and the end portions of the iron cores are connected by the yoke. As a result, a magnetic circuit, as continued by the paired iron cores, the yoke and the moving iron member, is formed to provide a switching device obtained having a low magnetic resistance and a small power consumption.
In an embodiment of the invention, moreover, neck portions formed just below the magnetic pole portions of the iron cores may be press-fitted in press-fit holes formed in the bottom face of the sealing case, and the press-fit holes may be clamped at their open edge portions between the open edge portions of cylindrical members press-fitted on the neck portions and the magnetic pole portions of the iron cores. The sealing case may be made of a material having a larger coefficient of thermal coefficient than that of the iron cores.
According to this embodiment, the sealing case is made of a material having a larger coefficient of thermal coefficient than that of the iron cores. Even if the temperature rises so that the iron cores expand, therefore, the expansion of the sealing case in the thickness direction is larger than those of the iron cores so that the open edge portion of the sealing case is firmly clamped between the magnetic pole portions of the iron cores and the open edge portions of the cylindrical members.
Even if the temperature drops so that the iron cores shrink, on the other hand, the shrinkage of the press-fit holes of the sealing case in the diametrical direction is larger than those of the iron cores so that the sealing case fastens the neck portions of the iron cores. As a result, there is obtained an effect that to provide a closed type switching device, in which the gas-tightness is not deteriorated even if the temperature changes.